The present invention relates generally to semiconductor fabrication and, more particularly, to a method for monitoring a semiconductor wafer during a spin drying operation, a method for spin drying a semiconductor wafer, and an apparatus for spin drying a semiconductor wafer.
In the fabrication of semiconductor devices, a variety of wafer preparation operations are performed. In conventional wafer cleaning systems, the wafers are scrubbed in a brush station, which typically includes a first brush box and a second brush box. A wafer is first scrubbed in the first brush box in a solution containing specified chemicals and deionized (DI) water. After being moved into the second brush box, the wafer is again scrubbed in a solution containing specified chemicals and DI water. The wafer is then moved into a spin, rinse, and dry (SRD) station where DI water is sprayed onto the top and bottom surfaces of the wafer as the wafer is spun. Once the wafer has been thoroughly rinsed, a spin drying operation is performed to dry the top and bottom surfaces of the wafer.
The spin drying operation must thoroughly dry the top and bottom surfaces of the wafer. If the spin drying operation is stopped prematurely, i.e., before the surfaces of the wafer are thoroughly dry, then the fluid remaining on the surfaces of the wafer may adversely affect subsequent fabrication operations. On the other hand, if the spin drying operation lasts longer than necessary to dry the surfaces of the wafer thoroughly, then the throughput productivity of the wafer cleaning system suffers. In conventional wafer cleaning systems, spin drying operations are not monitored to determine precisely when the surfaces of the wafer are thoroughly dry. Consequently, these wafer cleaning systems run the risk of either stopping the spin drying operation prematurely or unnecessarily extending the length of the spin drying operation.
In view of the foregoing, there is a need for a method for determining precisely when the surfaces of the wafer are thoroughly dry in a spin drying operation. In addition, there is a need for a method and apparatus for spin drying a semiconductor wafer that enables the spin drying operation to be stopped precisely when the surfaces of the wafer are thoroughly dry.
Broadly speaking, the present invention fills these needs by providing methods for monitoring a semiconductor wafer during a spin drying operation to determine precisely when the surface (or surfaces) of the wafer are dry. The present invention also provides methods and apparatus for spin drying a semiconductor wafer that enable the spin drying operation to be stopped precisely at the xe2x80x9cendpointxe2x80x9d of the operation, i.e., the point at which the surface (or surfaces) of the wafer are dry.
In accordance with one aspect of the present invention, a first method for monitoring a semiconductor wafer during a spin drying operation is provided. In this method, a capacitance value between a capacitance sensor and the wafer is measured as the wafer is being spun to dry a surface thereof. When it is determined that the measured capacitance value has reached a substantially constant level, a signal is generated indicating that the surface of the wafer is dry. In one embodiment, spinning of the wafer is stopped in response to the signal.
In accordance with another aspect of the present invention, a first method for spin drying a semiconductor wafer is provided. This method includes spinning the wafer to dry a surface thereof. As the wafer is spinning, the capacitance value between a capacitance sensor and the wafer is measured. When it is determined that the measured capacitance value has reached a substantially constant level, a signal is generated. In response to the signal, spinning of the wafer is stopped.
In accordance with a further aspect of the present invention, a second method for monitoring a semiconductor wafer during a spin drying operation is provided. In this method, light is directed toward a surface of the wafer as the wafer is being spun to dry a surface thereof. The light is directed such that the light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The intensity of the light reflected off of the surface of the wafer is measured. A signal indicating that the surface of the wafer is dry is generated when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry.
In one embodiment, spinning of the semiconductor wafer is stopped in response to the signal. In one embodiment, the measured intensity of light reflected off of the surface of the wafer when the surface is dry is determined in a calibration operation.
In accordance with a still further aspect of the present invention, a second method for spin drying a semiconductor wafer is provided. This method includes spinning the wafer to dry a surface thereof. As the wafer is spinning, light is directed toward a surface of the wafer such that the light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The intensity of the light reflected off of the surface of the wafer is measured. A signal indicating that the surface of the wafer is dry is generated when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry. In response to the signal, spinning of the wafer is stopped. In one embodiment, the measured intensity of light reflected off of the surface of the wafer when the surface is dry is determined in a calibration operation.
In accordance with yet another aspect of the present invention, a first apparatus for spin drying a semiconductor wafer is provided. The apparatus includes a hollow core spindle having a central opening therethrough. A chuck assembly is mounted on the spindle. The chuck assembly has a central opening therethrough and includes grippers for supporting a wafer at an edge thereof. A sleeve is disposed in the central opening of the hollow core spindle such that an upper end thereof extends through the central opening of the chuck assembly. A manifold is disposed in the upper end of the sleeve. A capacitance sensor configured to measure a capacitance value between the wafer and the capacitance sensor is affixed to the manifold. In one embodiment, the apparatus further includes a processor for determining when the capacitance value measured by the capacitance sensor reaches a substantially constant level.
In accordance with a still further aspect of the present invention, a second apparatus for spin drying a semiconductor wafer is provided. This apparatus includes a spindle and a chuck assembly mounted on the spindle. The chuck assembly includes grippers for supporting a wafer at an edge thereof. An arm having a capacitance sensor mounted thereon is positioned such that the capacitance sensor is disposed above a space to be occupied by a wafer that is supported by the grippers. The capacitance sensor is configured to measure a capacitance value between a wafer supported by the grippers and the capacitance sensor.
In one embodiment, the apparatus further includes a processor for determining when the capacitance value measured by the capacitance sensor reaches a substantially constant level. In one embodiment, the arm is movable so that the position of the capacitance sensor relative to the space to be occupied by a wafer that is supported by the grippers can be varied. In one embodiment, the arm has a plurality of capacitance sensors mounted thereon. Each of the capacitance sensors is disposed above a space to be occupied by a wafer that is supported by the grippers, and each of the capacitance sensors is configured to measure a capacitance value between a wafer supported by the grippers and the capacitance sensor.
In accordance with yet another aspect of the present invention, a third apparatus for spin drying a semiconductor wafer is provided. This apparatus includes a spindle and a chuck assembly mounted on the spindle. The chuck assembly includes grippers for supporting a wafer at an edge thereof. The apparatus further includes an arm having a light source and a detector mounted thereon. The light source is positioned to direct light toward a surface of a wafer being supported by the grippers such that light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The detector is positioned to measure an intensity of the light reflected off of the surface of the wafer.
In one embodiment, the apparatus further includes a processor for determining when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry. In one embodiment, the arm is movable so that the position of the light source and the detector relative to the surface of the wafer can be varied. In one embodiment, the arm has a plurality of light sources and a corresponding number of detectors mounted thereon. Each of the light sources is positioned to direct light toward a surface of a wafer being supported by the grippers such that light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the semiconductor wafer. Each of the detectors is positioned to measure an intensity of the light from a corresponding light source that has reflected off of the surface of the wafer.
The methods and apparatus of the present invention minimize the risk of either stopping a spin drying operation prematurely or unnecessarily extending the length of a spin drying operation. Thus, the methods and apparatus of the present invention advantageously improve the yield and throughput productivity in the manufacturing of semiconductor devices.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.